This members-only tutorial provides the steps to add custom PHP, JS and CSS code to output parent terms of a given taxonomy (like product_cat for example) and for each term, display a list of child terms if present with the list items' text linking to the corresponding term archives in Oxygen.
Step 1
Add a Code Block.
(optional) If the Code Block is not present inside a Column having a fixed width, you may want set it a width of say, 300px or higher depending on the length of your taxonomy terms.